Bug#880109: diffoscope: Pony wanted: git mode

[Axel Beckert]

Package: diffoscope
Version: 87
Severity: wishlist

Hi,

after the discussion around strip-nd's png backend, I tried
"strip-nondeterminism -t png t/fixtures/png/tEXt.png.in" in a checkout
of strip-nd's git repository.

Now the file t/fixtures/png/tEXt.png.in is locally modified:

→ git status --short
 M t/fixtures/png/tEXt.png.in

I would like to be able to use diffoscope to show the difference between
the checked in version and the local (or staged) version of a binary
file.

So I tried

→ git diff --binary | diffoscope
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/diffoscope/main.py", line 412, in main
    sys.exit(run_diffoscope(parsed_args))
  File "/usr/lib/python3/dist-packages/diffoscope/main.py", line 377, in run_diffoscope
    difference = load_diff(sys.stdin, "stdin")
  File "/usr/lib/python3/dist-packages/diffoscope/readers/__init__.py", line 31, in load_diff
    return JSONReaderV1().load(fp, path)
  File "/usr/lib/python3/dist-packages/diffoscope/readers/json.py", line 32, in load
    raw = json.load(fp)
  File "/usr/lib/python3.6/json/__init__.py", line 299, in load
    parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)
  File "/usr/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

but it bails out as shown above.

I can imagine three ways of calling diffoscope to provide such a
feature:

1) Maybe least effort, at least for diffoscope's CLI:

   Make "git diff --binary | diffoscope" work, i.e. make it understand
   git binary patches, at least while being inside the according git
   repository (not sure if that's necessary).

2) Maybe even easier to implement (doesn't need to understand git binary
   patches) and would contain a nice CLI:

   diffoscope --git [file […]]
   diffoscope --git --cached [file […]] (for staged changes)

3) Really super cool solution:

   Provide a git diff plugin which outputs diffoscope output instead of
   "Binary files a/t/fixtures/png/tEXt.png.in and
   b/t/fixtures/png/tEXt.png.in differ". :-)

   (That's the Pony I would like to have. :-)

-- System Information:
Debian Release: buster/sid
  APT prefers unstable
  APT policy: (990, 'unstable'), (980, 'unstable-debug'), (600, 'testing'), (111, 'buildd-unstable'), (111, 'buildd-experimental'), (110, 'experimental'), (105, 'experimental-debug')
Architecture: amd64 (x86_64)

Kernel: Linux 4.13.0-rc7-amd64 (SMP w/4 CPU cores)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE=C.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages diffoscope depends on:
ii  python3                3.6.3-2
ii  python3-distro         1.0.1-2
ii  python3-libarchive-c   2.1-3.1
ii  python3-magic          1:5.32-1
ii  python3-pkg-resources  36.2.7-2

Versions of packages diffoscope recommends:
ii  acl                              2.2.52-3+b1
pn  apktool                          <none>
ii  binutils-multiarch               2.29.1-6
ii  bzip2                            1.0.6-8.1
ii  caca-utils                       0.99.beta19-2+b2
ii  colord                           1:17
ii  default-jdk [java-sdk]           2:1.8-59
ii  default-jdk-headless             2:1.8-59
pn  device-tree-compiler             <none>
pn  docx2txt                         <none>
pn  enjarify                         <none>
pn  fontforge-extras                 <none>
pn  fp-utils                         <none>
ii  genisoimage                      9:1.1.11-3+b2
ii  gettext                          0.19.8.1-4
ii  ghc                              8.0.2-10
ii  ghostscript                      9.22~dfsg-1
pn  giflib-tools                     <none>
ii  gnupg                            2.2.1-5
ii  imagemagick                      8:6.9.7.4+dfsg-16
ii  imagemagick-6.q16 [imagemagick]  8:6.9.7.4+dfsg-16
ii  jsbeautifier                     1.6.4-6
ii  libarchive-tools                 3.2.2-3.1
pn  llvm                             <none>
pn  mono-utils                       <none>
pn  odt2txt                          <none>
pn  oggvideotools                    <none>
ii  openjdk-8-jdk [java-sdk]         8u144-b01-2
ii  openssh-client                   1:7.6p1-2
ii  pdftk                            2.02-4+b2
ii  pgpdump                          0.31-0.2
ii  poppler-utils                    0.57.0-2
pn  python3-argcomplete              <none>
pn  python3-binwalk                  <none>
ii  python3-debian                   0.1.31
ii  python3-defusedxml               0.5.0-1
pn  python3-guestfs                  <none>
pn  python3-progressbar              <none>
ii  python3-rpm                      4.12.0.2+dfsg1-2+b1
ii  python3-tlsh                     3.4.4+20151206-1+b3
pn  r-base-core                      <none>
ii  rpm2cpio                         4.12.0.2+dfsg1-2+b1
pn  sng                              <none>
ii  sqlite3                          3.20.1-2
ii  squashfs-tools                   1:4.3-4
ii  tcpdump                          4.9.2-1
ii  unzip                            6.0-21
ii  vim-common                       2:8.0.1226-1
ii  xxd                              2:8.0.1226-1
ii  xz-utils                         5.2.2-1.3

Versions of packages diffoscope suggests:
ii  libjs-jquery  3.2.1-1

-- no debconf information